1. Field
Example embodiments relate to flash memories. More particularly, the example embodiments are concerned with a flash memory device capable of providing a pass voltage with various levels and a programming method thereof.
2. Description of the Related Art
In recent years, flash memory devices have been interested in the necessity of assuring pass voltage windows along the shrinking-down of design rule.
In a programming operation of a flash memory device, a program voltage is applied to a selected word line while a pass voltage is applied to unselected word lines.
Program voltage disturbance caused by a low pass voltage results in a malfunction that program-inhibited memory cells, among pluralities of memory cells, coupled to a word line to which the program voltage is applied fail during programming. Pass voltage disturbances, caused by a high pass voltage, result in a malfunction of memory cells to which the pass voltage is applied. Pluralities of memory cells coupled to the same cell string, fail during programming.
In other words, the pass voltage window means a proper range of the pass voltage without the pass voltage disturbances and the program voltage disturbances. Therefore, a broad pass voltage window enhances the reliability of the flash memory device.
However, in practice a pass voltage window is only determined after fabricating a wafer including flash memory devices. An insufficient pass voltage window generates a need to modify a programming method several times by way of revision, which delays a development term or turnaround time of the flash memory devices.